In the textile industry, there are many production machines in which a large number of production units are in operation at the same time. As examples may be mentioned spinning machines, bobbin winding machines and yarn twisting machines. There is an obvious need for automatic monitoring of each individual production unit for the smooth progress of production and the quality produced. For checking the production process, the most important factor to monitor is thread breakage, and for quality control the most important factor is the cross-section of the twisted yarn which serves as a check on whether all the threads have been twisted in.
Although the term "thread" is consistently used in the following description, it should be understood to include all products of spinning, such as yarns, twisted threads or yarns, strands, filaments, and the like.
The above-mentioned monitoring of all the individual production units could be technically solved with known means but has hitherto not been realized on account of the costs involved. Owing to the large number of production units only a minimum expenditure of cost per production unit would be affordable if the cost per machine is to be kept within acceptable limits.
For detecting thread breakage in ring spinning machines, installations which have so-called travelling sensors have recently appeared on the market. These are able to monitor the movements of the ring traveller of a whole side of a ring spinning frame with a single sensor. This solution is acceptable from the point of view of cost for detecting thread breakage but it cannot be used for measuring other thread parameters because the signal is produced by the rotating ring traveller and not by the thread itself.
No economically feasible solutions have hitherto been found for determining the thread cross-section and/or its non-uniformity directly at the production unit of ring spinning frames, twisting frames, and the like.